SOLUTION

A carpenter constructed a rectangular sandbox with a capacity of 10 cubic feet. If the carpenter were to make a similar sandbox twice as long, twice as wide, and twice as high as the first sandbox, what would be the capacity, in cubic feet, of the second sandbox?

(A) 20
(B) 40
(C) 60
(D) 80
(E) 100

Since given that \(volume=L*W*H=10\), then \(new \ volume=(2L)*(2W)*(2H)=(2*2*2)*(L*W*H)=8*10=80\).

Answer: D.
_________________

Let x,y & z be L,W & H
so xyz = 10 cu ft
As per question if we double the lengths on all dimensions
we get (2x)(2y)(2z)=8 xyz= 8*10= 80
Answer: D

volume =l*b*h =10 cubic feet
Now we have twice as long, twice as wide, and twice as high as the first sandbox,
L=2*l
B=2*b
H=2*h
final volume =L*B*H =2*l*2*b*2*h=8*(l*b*h) =8*10=80 cubic feet

answer is D

V=LWH

Original Volume = 10

In order to keep things simple. I made Height = 5, Length = 2, and Width = 1

The second statement says double everything.

Height = 10, Length = 4, and Width = 2

V = 80

A quick note on doubling. When you double a length you have 2*L1. When you double all lengths of a rectangle you have (2*L1)(2*L2) = A. An increase of 2^2 or 4. When you double all lengths of a rectangular prism you have (2*L1)(2*L2)(2*L3) = V. An increase of 2^3 or 8.

This leads to the basic relationship:

Line: 2*original size
Rectangle: 4*original size
Rectangular Prism: 8*original size

You can do the math out or memorize this relationship to speed things up.

Answer = (D) 80

Original volume = 10 cubic feet

All 3 dimensions made "twice"

New volume = 10 * 2 * 2 * 2 = 80

We are given a rectangular sandbox with a given capacity, which is the volume of the sandbox.

Therefore, we know that the volume of the sandbox is: (L)(W)(H) = 10 cubic feet

We then are told that the carpenter doubles the length, the width, and the height. We can represent this doubling as (2L)(2W)(2H). Thus

(2L)(2W)(2H) = (2)(2)(2)(L)(W)(H) = (2)(2)(2)(10) = 80 cubic feet

Answer D.
_________________

Using some simple values, let all sides be equal to 2. The first surface area will be 2*2*2 = 8
Now double all these sides. The new surface area will be 4*4*4=64
64 is 8*8. Hence the answer should be 10*8=80 or D

I have a small doubt in this question. The volume of a rectangular solid is l*w*h=10*10*10 because the question says its cubic feet. Where am i going wrong in my concept??

We are told that the volume is 10 cubic feet (the volume of 3-D objects is measured in cubic units), not that the lengths of the sides are 10 feet, so it should be l*w*h = 10. Please re-read the solutions above.
_________________

Thank youBunuel.

This may is more of a conceptual question I guess. In 2l *2b*2h can we not take the 2 common such as 2(L*B*H).

L*B*H=10.....-> given.

2L*2B*2H= ?
2(L*B*H)
2(10)=20
_________________

I have a similar question. Why are we not taking the common factor 2(L*B*H)?

Hi dixxa,
Common factors are to be factored out when the terms are either added or substracted in an equation/expression. In case of multiplication or division, it is simply multiplication or division of terms respectively.

Here, in 2L*2B*2H, we have three terms multplied 2L, 2B, and 2H.


From 2L, 2 can be factored out. (you know 2L=2 multiplied by L)

Similarly, From 2B, 2 can be factored out.
Similarly, From 2H, 2 can be factored out.

Now, 2L*2B*2H=2*2*2*L*B*H=8(L*B*H)

Had it been 2L+2B+2H, then we can factor out 2 as '2' is a common factor of 2L, 2B, and 2H, making 2L+2B+2H=2(L+B+H)


Hope it clarifies your query.
_________________

Thank you so much for your explanation. It makes sense.

If each of the sides was increased by a factor of 2,

then the linear ratio is 1:2. In order to get the volume ratio, I need to

cube the linear ratio; so the volume ratio is going to be (1 cubed), to (2 cubed) -- which is 8.

So if this is 10 cubic feet, this is going to be 80 cubic feet, and the correct answer choice is D.
_________________

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________